Royal Society. 59 



instead of "acids/' or "electro-positive" instead of "bases"; 

 for how are we to define electro-negative, except as the opposite 

 of electro-positive, or electro-positive, except as the opposite of 

 electro-negative? Gerhardt's definition of acids, taken alone, 

 certainly does not tell us much more than most other definitions 

 of chemical terms ; but it seems to me to state accurately the 

 relation in which acids stand to other salts. 



I will allude to only one other portion of Professor William- 

 son's paper. One of the objections to the use of the term acid 

 in Gerhardt's sense, which he brought forward in his communi- 

 cation to the Chemical Society, was that the action of the com- 

 pound HNO 3 upon the compound HKO cannot be described as 

 a combination of nitric acid with potash, without concealing the 

 fact that what takes place is truly a double decomposition. In 

 answer to this, I pointed out that, even with the definitions of 

 acids and bases which Professor Williamson advocates, the 

 action which takes place between these bodies must often be 

 described as a double decomposition, and I instanced the action 



C 2 H 3 01 

 of water upon the compounds (C 2 H 3 0) 2 0, n7TJ5Q fO, and 



(C 2 H 3 O) 2 S. I foresaw at the time the reply, that double 

 decompositions, "in which the resulting molecules are less various 

 than the original molecules," are to be regarded as processes of 

 combination ; and it was precisely for this reason that I adduced 

 the second and third of the above instances, instead of being 

 content with the first only. 



I am, Gentlemen, 



Your obedient Servant, 



G. C. Foster. 



X. Proceedings of Learned Societies.™ 



ROYAL SOCIETY. 



[Continued from vol. xxix. p. 550.] 



May 4, 1865. — Major General Sabine, President, in the Chair. 



HP HE following communication was read : — 



*• " On the Rate of Passage of Crystalloids into and out of the 

 Vascular and Non-Vascular Textures of the Body." By Henry 

 Bence Jones, A.M., M.D., F.R.S. 



The paper is divided into five sections — 



1st. On the method of analysis, and its delicacy. 



2nd. Experiments on animals to which salts of lithium were given, 

 upon the rate of their passage into the textures. 



3rd. On the rate of the passage of lithium-salts out of the textures. 



4th. Experiments on healthy persons, and on cases of cataract. 



5th. On the presence of lithium in solid and liquid food. 



